The coating of solid dosage forms such as tablets and pills has long been known in the prior art. Coatings are commonly applied to such dosage forms for one or more of the following reasons: to protect the ingredients against the atmosphere, to mask unpleasant taste and odor, to improve the appearance of uncoated tablets and pills, to control the site of action of the drug and to prevent incompatabilities when two or more pharmaceutically active ingredients are incorporated into a single dosage form. Numerous coating solutions are powders have been used over the years in the coating of tablets including polymers or acrylic acid or acrylic acid derivatives as well as other polymeric substances, such as shellac, cellulose derivatives, polyvinylpyrrolidone, polyethyleneglycol, copolymers or polyvinylpyrrolidone and polyvinylacetate, silicon resins and the like. Although the coating of tablets and pills can be effected relatively easily by known processes owing to their porous surfaces which readily adhere to such coating substances, difficulties arise when coating soft gelatin capsules because of their smooth, nonabsorptive surfaces and flexibility or elasticity.
Many attempts have been made to produce improved coating capsules. In particular, several attempts have been made to produce stable enteric coated soft gelatin capsules which resist dissolution in the acid secretions of the stomach and dissolve or disintegrate primarily in the alkaline secretions of the intestines.
Enteric coated soft gelatin capsules are desirable for the administration of liquid medications which are distasteful to the patient, or for drugs which cause nausea or gastric distress, or which are unstable in the acid environment of the stomach. In addition, enteric coatings are useful for producing a delayed action of a drug or to deliver medication to the intestinal tract when this is the intended site of action.
Accordingly, a main object of the present invention is to provide a new process for enterically coating soft gelatin capsules which exhibit superior mechanical strength, and improved environmental stability.